Photographic surveying



Feb. 17, 193l. H, Q FOUCADE 1,793,217

PHOTOGRAPHIC SURVEYING Filed Feb. 26. 1927 4 Sheets-Sheet l ,A iff@ f cz] 1/ JY mfenm."

HENRY GEORGES FoufzcADr;

Feb. 17, 1931. H, G, FOURC'ADE 1,793,217

PHOTOGRAPHIC SURVEYING Filed Feb. 26. 1927 4 Sheets-Sheet 2 l l l l lHENRY Geoaif FJURCADF.

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Feb. 17, 1931.

H. G. FURCADEY PHOTOGRAPHIC SURVEYING Filed Feb. 2e. 1927 4 Sheets-Sheet5 Hcnnj Georges Fou rcade l NVENTOR 'u ATYORNEY.

Feb. 17, 1931. H. G. FoURcADE PHOTOGRAPHIC SURVEYING Filed Feb. 26. 19274 Sheets-Sheetl 4 Henrlj Georges furcndc INVENTOR ATTORNEY Patented.Feb. 17, 193i HENRY GEGRGES FOURCADE, OF HUMANSDOB?, CAPE COLONY, SOUTHAFB/ICA PHOTOGRAPHIC SURVEYING Application led February 26, 1927, SerialNo. 171,325, and in. Great Britain July 19, 1926.

'.lhis invention relates to a device and method for determining theposition in space ot' points shown on a pair of serial photographs,taken from two different points of View, and

5 for tracing on a plane surface a map of the surface represented.Several devices of the kind have hitherto become known. rl`he setting ofphotographs in those devices has always required a prior knowledge ordetermination, of the relative positions in space in exposure, withoutany necessary prior knowledge or determination of the correspondence,

9 and to provide novel and simpler means for measuring elements of thesurface represented, or for producing a map of the surface. y

.The method employed is based upon the following new theorem: Thecorrespondence between the pencils of rays joining two centres to anynumber of points in space is uniquely determined if to five rays of theone there are given five rays in the other, provided no three pairs ofthe rays lie in a plane.

According to this invention the device has the followingv characteristicfeatures. Two photogoniometers, carrying photographs obtained as theresult of exposures and objectives disposed in the centre of projectionof the photographs, are mounted so that each of them can be turnedseparately about a polar axis, common to both, which is convenientlydisposed horizontally, and also about a declinat-ion axis normal to thispolar axis and parallel to the plane of the plate, while, :Eurther, eachplate can be rotated, in its own plane about an axis passing through thecentre of its photogoniometer lens and normal to the plane of the plate.These movements allow the plates to be set at any inclination ororientation to each other, and, particularly, so as to bring the imageson these plates in correspondence. Light rays passing through the platesand lenses of the photogoni-ometers are reflected by means of mirrors,or prisms,

into a. fixed binocular telescope, provided with s1ghting marks, wherethey combine to form a stereoscopic image. The mirrors or prisms aremounted on slides arranged to move parallel to the polar axis and, bydisplacing the slides suitably, the stereoscopic image can be traversedacross the field of vision in one direction, while traversing the imagein a direction at right angles is effected by swinging the twophotogoniometers similarly and simultaneously together around the polaraxis. These movements enable any portion 0f the stereoscopic picture tobe brought into the field of vision and, in consequence, the sightingmarks in the telescope can be located over any place in the image.Graduation on circles, arc, or otherwise arranged, enable readings to beobtained of the various movements imparted to parts of the apparatus.

The following is a convenient arrangement which may be adopted for themirror system bymeans of which the rays from the photogoniometers arereflected into the telescope. On each of the slides moving along fixedguides parallel toy the polar axis are mounted two mirrors of suitableconstruction one of these mirrors being fixed and disposed so astoreflect light rays which fall upon it into one of the telescopelenses. Adjacent to the fixed mirror there is mounted a second mirroradapted to reflect light rays passing through the lens of thephoto-gouiometer into the fixed mirror. This second mirror can swingabout a vertical pivot and is connected, by means of gearing, pulleys,or other suitable mechanism, with a lever, also pivoted vertically onthe slide, in such manner that the angular movement of the lever aboutits axis is always double that of the mirror about its axis. This leverpasses through a guide carried on a fixed vertical pivot in the verticalof the polar axis. The distance between the axis of this pivot and thedeclination axis of the photogoniometer is made equal to the distancebetween the centres about which the lever and the mirror respectivelyare pivoted on the slide, while a line between these two pivot centreson the slide is parallel to the polar axis. In consequence the angularmovement of the mirror will be always half that of a line between thepivot centre of the mirror and the declination axis of thephotogoniometer, so that rays of any incidence through this declinationaxis, which passes substantially through the front nodal oint of thelens, will be reflected by the plvoted mirror in a constant directioninto the fixed mirror and thence to the telescope.

The angle which the sighting line makes with the polar axis is thengiven by double the amount of rotation of the pivoted mirror, reckonedfrom a suitable index.

lf the longitudinal guides are made suiii- J ciently straight it isfurther possible to disense with the fixed mirrors and to arrange 'orthe rays from each photogoniometer to be reflected directly into thecorresponding telescope objective. ln that case the right angles prismswhich would otherwise be employed within the telescope are replaced bydouble reflection prisms in order to preserve the erection of the image.

ln the absence of a knowledge of the vertical, plates which weresubstantially horizontal when exposed, although the can be utilized, arenot so well conditione for setting into correspondence as are inclinedplates. :inclined plates are therefore as a rule preferable.

To set a pair of plates into correspondence it is necessary andsufficient to bring five suitable points common to the two plates intocorrespondence, that is to say, to make both images of each point appearat the same height in the field of view of the respective telescope.

Turning now to the mapping system, this may be constructed in thefollowing manner. Two rods which may be called the mapping rods areconnected by means of a cardan joint to a pencil carrier which can movefreely over the surface of a drawing board. These two rods are somounted that they can swing together about an axis parallel to the polaraxis of the main part of the apparatus. A coupling member is providedbetween the mapping rods and the pair of photogoniometers such that, asthe rods are swung about their parallel axis, the pair ofphotogoniometers swing similarly about their polar axis. Each of themapping rods passes first through a pivoted guide sleeve on the parallelaxis and secondly through a similar sleeve carried by caliper-likemembers which can slide along a path parallel vto the parallel axis. Theends of the caliper-like members turn down to the parallel axis and areconnected by rods to the slides of the main a paratus on which themirrors are mounte so as to make the displacement of each mirror slideconstantly equal to that of the end of the corresponding caliper-likemember.

The two guide sleeves carried by the caliper-like members are maintainedat the same maaar? constant distance from the parallel axis, thisdistance being equal to the distance between the polar axis of the mainapparatus and the axis of the lever which is pivoted on the slidingmirror carrier referred to above.

lf now the device has been properly set and since rotation of the pairof p otogoniometers about the polar axis will cause similar andcorresponding rotation, about the parallel axis, of the plane in -whichlie the ma ping rods, and by reason of the connections etwecn thesliding caliper-like members and the sliding mirror carriers of the mainapparatus it fol' lows that provided the sighting mark is maintained onthe surface of the apparent optical model, the pencil point will tracein space a copy of the optical model to any scale, within the range ofthe apparatus, determined by the ratio of the distance between the pivotcentres of those guide sleeves for the mapping rods which lie on theparallel axis of he mapping system, to the length of the ase. Y

The details of construction may be modified as found desirable in orderto adapt the apparatus for particular uses.

Referring to the accompanying drawings,

Figures 1 5 show a constructional example of a device according to theinvention for measuring, and copymg on a plane surface, linear elementsof the surface to be obtained from a pair of photographs of a spatialform.

Figure l is a side elevational view of the left half of the machine,certain parts being omitted for the sake of clearness.

Figure 2 is a similar view of the right half of the machine.

Figure 3 is a plan view of the left half of the machine.

Figure 3A is a plan view of the right half of the machine.

Figure 4 a section on line 4-4 of Figure 2, and

Figure 5 an end elevation (if the upper part of the apparatus.

rlwo photogoniometers A hold a pair of photographic plates a1 obtainedas the result of exposures, and are mounted on a frame b1 in such mannerthat each can be turned separately about a common polar axis ofrotation, determined by pivots c1 which are disposed horizontally and inalignment and also about a declination axis, determined by the pivotsd1, which is at right angles to the polar axis and parallel to the planeof the plate. Further each plate can be turned in its own plane, byrotating the position circle el on which it is carried, about an axiswhich is normal to the plate and at right angle to the declination axisof its photogoniometer. The three axes about which the plate can bem'oved pass throu h, or close to, the front nodal point of the lens f1of its photogoniometer, the back nodal point of this lens being at thecentre of projection of the photograph.

The pivots c1 of the frames b1 rest in uprights g1 carried by the baseplate plate B.

In front of the polar axis, and parallel to it, are-mounted, on the baseplate B, two guide bars h1 on which two slides '1 move longitudinally.Each of the slides carries a fixed mirror jl, another mirror ul rotatingabout a vertical axis Z1, an index arm m1 moving with the mirror 761 anda graduated arc of circle nl on which the angular rotation of the mirrork1 may be read. Further, on each slide is disposed a lever arm o1pivoted at p1,

the free end of which passes through a guide sleeve g1 pivoted at afixed point 7'1 on the stand of the instrument. The pivot r1 is in thevertical of the polar axis, and the distance between the axis of thispivot, which is vertical, and the declination axis of the correspondingphotogoniometer is equal to the distance between the centers p1 and Z1about which the lever 01 and the mirror k1, respectively', are pivotedon the slide, while a line between these two pivot centres p1 and Zl isparallel to the polar axis.. The rotation of the mirror k1 isconstrained to be always half that of the lever 01, by means of twopulleys or segments of pulleys s1 and t1, the radius of the segment s1being double that of the pulley t1. The two pulleys are connected by asteel band or other form of belt u1, fixed to both and kept in propertension by means of a cord al, also attached to the pulleys,which-'passes round two wheels 'w1 and is kept taut by a spring m1.

Light rays passlng through the plates and lenses of the photogoniometersare reflected by the mirrors jl and k1 into the fixed binocu-4 lartelescope y1 consisting of two objectives el two single reflectionprisms a2 a pair of sighting marks b2 and a pair of eyepieces 02. Thesetting of each photogoniometer about its declination axis is effectedby means of the screws d2 which are omitted from Figure 1 for the sakeof clearness. The setting about the polar axis of the left handphotogoniometer relatively to theright hand photogoniometer is effectedby means of the differ ence screw e2, the graduated arc of circle f2 andthe index mark g2. The setting about the polar axis of the pair ofphotogoniometers relatively to the mapping system is effected by meansof the levelling screw h2, the graduated are of circle 2 and the indexmark y?, and the settings in position angle of the two plates iseffected by rotating the graduated position circles e1 relatively to theindex marks 762. The graduated are of circle fw1 serves to measure thecommon rotation of the pair of photogoniometers after they have been setin correspondence.

The mapping system is constructed in the following manner. A carrier Z2(Fig. 1) is provided for a pencil m2, this carrier being smooth andplane on the under surface, so as to move freely over the surface of asheet of paper disposed on the drawing board n which is accuratelyplane. The ends of two rods o2 are connected by means of a cardan jointp2 with one axis at right angles to the plane of the rods and the centreof rotation of the cardan joint in the line of the pencil lead. Thesetwo rods, which may be termed the mapping rods, diverge and pass throughsleeves g2 and r2 which are pivoted, on a transverse member 82,perpendicularly to the plane of the rods and in the line of the axis ofrotation of the transverse member, determined by the pivots t2 at itsends.

The transverse member s2 is formed of a pair of slotted guide barsdisposed on either side of the mapping rods o2 and connected together atthe ends which carry the pivots t2. The axis of rotation of thistransverse member is disposed parallel to the polar axis of theinstrument and may be termed the parallel axis. The pivots of thetransverse member rest in nprights u2 arising from the base plate B. Thepivots ofthe sleeve g2 are fixed to the transverse member. The othersleeve r2 is pivoted on a movable sliding box 02. The distance betweenthe pivot centres of these two guide sleeves can therefore be adjustedby displacing the box v2 with its guide sleeve r2 along the slot v4 inthe transverse member of the mapping system.

Two caliper members w2 m2 are provided which can slide relatively andalso along the transverse member s2. The sliding movement of thesecaliper members is parallel to each other and to the parallel axis ofthe mapping systern, the caliper members being disposed on the side ofthe parallel axis remote from the pencil carrier. Each of the calipermembers, which consist of a pair of rules, suitably braced together andbetween which the rods 02 pass, is provided with an end turned at rightangles to its main part and the points y2 z2 of these turned down ends,which lie in the parallel axis, are connected by means of pairs ofdistance rods a3 b3 which are shown on Figures 3 and 5 (but are omittedfrom Figure l for the sake of clearness) disposed parallel to the polaraxis, and cross heads c3 d3 which in Figure 2 are only shown in section,with the slides of the main apparatus, on which are mounted the mirrors.The connection between the cross-heads and the caliper ends is effectedby studs at 'y2 and z2 against which the cross-heads are pressed by fiatsprings t4 (Figure 2) so that the caliper ends may swing freely with themapping rods o2 and the transverse member, about the parallel axis,without affecting the crossheads c3 d3 or the pairs of rods a3 b3attached to them, while at the same time the longitudinal motion of thecalipers is transmitted to the mirror slides of the main apparatus. Thepoint y2 is connected by the pair of rods a3 with the left hand mirrorslide, and the point zgby the pair of rods b with the right und mirrorslide.

On each caliper member is disposed a pivoted guide sleeve through whichpasses one of the mapping rods o. The left hand sleeve e3 is pivoted tothe box-like end f of a fixed arm of the lower caliper member fw. Theright hand sleeve gs is pivoted upon a boxlike slide It which may bedisplaced along the upper caliper member :v2 and fixed in any suitableposition by means of the clamping screws 8. The two guide sleeves e3 g8carried by the caliper memzbers are pivoted at an equal distance fromthe axis of the shaft terminated by the pivots Z2, t2 of Fig. 2, thisdistance being equal to the distance between the polar axis of the mainapparatus and the axis of the lever which is pivoted on each slidingmirror carrier of the main apparatus. The upper and lower surfaces ofthe caliper members and the upper surface of the transverse member beingall accurately plane and parallel this distance remains invariablewhatever the positions of the guides sleeves eS gs relatively to thetransverse member may be. Each of the box ends f3 71,8 which are ofequal thickness is pressed at a stud against a guide bar 7'5 by means ofspring rollers k3 carried by the box ends. The guiding ed e of this baris kept at a distance from the parallel axis equal to that of the ivotsof the sleeves e8 qa from the same axis y supports Z8 and m8 fixed tothe transverse member. On a prolongation of the middle support fmSi andin the plane of the axes of the mapping rods o2 is fixed a pivot 'as atan arbitrary distance from the parallel axis.

The coupling of the rotation of the plane of the mapping rods about theparallel axis with the rotation of the pair of photogoniometers aboutthe polar axis is effected in the following manner. A shaft o, disposedin the line of the polar axis and supported by uprights p3 arising fromthe base plate B, carries two arms g8 r3. The end of the arm g3 butsagainst the point of the levelling screw 71,2, previously referred to,which is attached to the frame of the right hand photogoniometer. Theother arm rs is disposed opposite the middle support m8 of the guide barof the mapping system and carries a pivot s3 of which the distance fromthe polar axis is made equal to the distance of the pivot n3 of thesupporting arm m8 from the parallel axis of the mapping system. Furthera coupling rod, or pair of rods t3, of which the lengths are equal tothe distance between the parallel and the polar axes of the instrument,connects the pivots s3 with the pivot n3. The two arms m and r3 formingwith the coupling rods t3, three sides of a parallelogram theirrotations and that of the pair of photogoniometers will be equal andsimilar.

The varying of the inclination and of the height ofthe drawing board nis effected in the following manner: -Four angle bars ua are attached tothe lower surface of the drawing board, perpendicularly to its plane andconnected at their lower ends Aby a plate 'v thus forming a kind of boxwith open si es. This box can slide up and down in another similar boxformed by a lower table 'w8 four angle bars ms and bracing members ya.The movement of the upper box out of the lower is regulated by means ofa screw .as which has a collar a in the centre of the lower table and anut b* in the centre of the bottom plate v8 of the upper box, but may beotherwise arranged. The inclination of the pair of boxes and thereforethat of the drawing boards is made adjustable by pivoting the lower boxat c* on uprights d4 from the lower base plate C of the apparatus. The

axis of the pivots c* is horizontal and in a plane perpendicular to thepolar axis. Two levelling screws e4 of which the nuts are fixed to thebase plate C serve to clamp the table at the desired inclination, whichis measured by a graduated arc of circle 7 attached to the lower tableand an index mark g4 attached to the lower base plate or vice versa.

To transmit the rotation of the screw actuating the rise and fall of thedrawing board to a conveniently placed hand wheel h* (Fig. l) thefollowing arrangement is devised: A shaft z" is disposed in the line ofthe pivots c* of the lower table. This shaft is supported by bearin s j*formed in projections from the lower ase plate C. At one end of thisshaft is keyed a bevel gear wheel la* which engages a similar bevel gearwheel Z* keyed to the head of the screw z3. also keyed a third bevelgear wheel m4 which engages a fourth similar wheel n* keyed to the endof a horizontal shaft o* which serves to transmit the motion to the handWheel L, a pair of spur gear wheels being interposed at p* to allow thehand wheel at the further end of an auxiliary parallel shaft, g4 to beraised to a convenlent level above the base plate C. The shaft i* beingin line with the pivots c* and this line passing through the axis of thegear wheel Z it follows that wheels k* and Z* will remain in mesh forany inclination of the drawing board resulting from the adjustment ofthe evelling screws e.

After the pair of plates have been set in correspondence the adjustmentof the mapping system is effected in the following manner. Firstly thelength of the base is set off, on the scale desired for the map, bysliding the box o2 to the appropriate reading of its graduated scale 1"which measures the separation of the pivot centres of the guide sleeves02 and r2. Thebox is then clamped in position by means of the screws s4.Secondly, the left hand mapping-rod is made vertical when the line ofcollimation of the left hand telescope is set perpendicularly to thepolar On this shaft is' axis, that is to say for 90 reading on thecircle of the corresponding mirror slide and the distance rod a3 clampedto the same slide. Thirdly, the right hand mapping rod is made verticalwhen the line of coll-imation of the right hand telescope is setperpendicularly to the polar axis and the box ha is then clamped to itscaliper by means of the screws i3. Fourthly, the pair of rods being setin a vertical plane, the pair of photogoniometers are rotated togetherround their polar axis by turning the screw h2 until the reading on theauxiliary arc 2 corresponds with the computed amount of rotation 0 whichwould be necessary to bring a trace on the photographs of the verticalplane of the base line into the horizontal measuring plane of theapparatus. Fifthly, the drawing board is set to the computed inclinationof the base line. The mapping system is now set for either drawingcontour lines at determinate heights read from a computed zero on theScale a4, the hand wheel h4 being in such case kept fixed for eachheight, or for drawing orthogonal projection of the topographicalfeatures, in which case the sighting marks are kept in apparent contactwith the features to be mapped by means of the hand wheel. In both casesthe necessary motion is also imparted to the mirror slides and to thepair of photogoniometers by moving with the right hand the pencilcarrier over the surface of the paper. If a cutting tool is substitutedfor the pencil a solid model may be carved by the tool.

Claims:

1. An apparatus for photographic surveying, in combination, a binoculartelescope provided with a mark system, two universally movablephotogoniometers each adapted to hold a photograph taken from lthe endsof a base line at different angles and-each carrying anv objectivedisposed in the centre of projection of the photograph, a set of plvotsin line forming a horizontal axis of rotation common to bothphotogoniometers and coinciding substantially with the line joining thefront nodal points of the two photogoniometer objectives, means forlmpartmg equal amounts of rotation of the two photogoniometers roundthis axis, and a refiectlng system comprising for each photogomometer aslide movable in a direction parallel to that of the commonphotogoniometer axis, a re lector mounted on a vertical axis of rotationon said slides, a horizontal lever also pivoted vertically-on saidslides, and means for c oupling the refiect'or with the lever and thesl1de, these means being adapted to impart to the reflector a rotationequal to half the amount of rotation imparted to the lever bylongitudinal motion of the slide.

2. An apparatus for photographic surveying, in combination a binoculartelescope provided with a mar system, two umversalfront lnodal points ofthe two photogoniomei ter objectives, means for imparting equal amountsof rotation of the two photogoniometers round this axis, a reflectingsystem comprising for each photogoniometer a slide movable in adirection parallel to that of the common photogoniometer axis, areflector mountedV on a vertical axis of rotation on said slides, ahorizontal lever also ivoted vertically on said slides, and means orcoupling the reflector with the lever and the slide, these means beingadapted to impart to the reiector a rotation equal to half the amount ofrotation imparted to the lever by longitudinal motion of the slide, anda mapping system comprising a drawing board, means for adjusting theinclination of the board to correspond with that of the base line, meansfor displacing the board in height while it remains parallel to itself,a copying tool moving freely over the plane of the drawing board, a pairof rods hinged together to the copying tool, sleeves through which saidrods slide, and a pair of pivots terminating in a shaft on which saidsleeves are disposed, said pivots determining an axis of rotationparallel to the axis of rotation determined b the pivots of thephotogoniometers, means or coupling the rotation of the plane of thepair of rods with the rotation of the pair of photogoniometers about thecommon axis determined by their pivots, these means being adapted tomake the two rotations constantly equal and similar, and means fortransmitting vto the respective slide of the mirror system thelongitudinal motion, in a. direction parallel to that of the axisdetermined by the photogoniometer pivots, of a point in the axis of eachrod at a constant distance from the parallel axis of rotation of therods, these means beino` adapted to make the two longitudinaldisplacements equal and similar.

In testimony whereof I aix my signature.

HENRY GEORGES FOURCADE.

